Microcircuits and
semiconductors are completely tested in packaged part form.
However, since our product is un-encapsulated die, we are unable to
test 100% of the electrical parameters necessary to ensure a
conforming device. In an effort to determine the performance of and
get a statistical probability of a diffusion lot of die, the hybrid
industry has established methods of lot acceptance testing
(LAT).
Lot acceptance testing is a sampling method used to discover if a
wafer lot has a reasonable probability that it will meet customer
specifications. LATs are performed upon customer request. The
request could be in the form of a source control drawing (SCD),
customer specification, and/or they may request Element Evaluation
per Appendix C of MIL-PRF-38534, Class H (for standard high
reliability) or Class K (for space level reliability).
When testing to MIL-PRF-38534 Class H, a 10 piece sample size is
used with 0 rejects allowed. The 10 packaged test samples are
pulled at random from the lot and subjected to the following
tests:
- Internal visual inspection
- Final electrical tests at +25°C., minimum and maximum operating
temperatures
- Wire bond evaluation (five die, ten wires)
MIL-PRF-38534, Class K requires a minimum of 10 samples, however 3
test samples from each wafer must be pulled and subjected to a more
stringent sequence of tests:
- Internal visual inspection
- Constant acceleration
- Temperature Cycling
- Interim electrical tests at +25°C., minimum and maximum
operating temperatures
- Burn-in (240 hours)
- Post burn-in electrical test at +25°C., minimum and maximum
operating temperatures
- Steady state life test (1,000 hours)
- Final electrical test at +25°C., minimum and maximum operating
temperatures
- Wire bond evaluation (five die, ten wires)
- Scanning electron microscopy (SEM) of one die from each
wafer
In the absence of customer supplied electrical test tables; we test
devices to the manufacturer data book or the military slash sheet
if one is available.
All requests for lot acceptance testing to either a customer's
specification and/or to military specifications must be reviewed by
component engineering. The component engineer will evaluate our
capability to screen the device to comply with the customer's
requirement.
